The MST, which is described in detail by Blum (1997), consists of foursensors: the magnetic susceptibility logger, gamma ray attenuationdensiometer (GRA),P-wave logger (PWL), and natural gamma raydetector (NGR). MST data were sampled at discrete intervals along thecore. The sample interval and the data acquisition period for eachsensor were set to optimize the resolution of data acquired within thesampling time available for each core. MST data are significantlydegraded if the core liner is only partially filled or if the core isdisturbed. When RCB or XCB drilling was used, the core diameter wasless than the nominal 6.6-cm core diameter. The reduced corediameter required corrections of the values measured by the MST. Thevalues in the database do not reflect these corrections, but the figurespresented in the following chapters show corrected data.

Magnetic Susceptibility Logger

Magnetic susceptibility is the degree to which a material can bemagnetized by an external magnetic field. If the ratio of magneticsusceptibility is expressed per unit of volume, volume susceptibility isdefined as

=M/H,

whereM

= the volume magnetization induced in a material ofsusceptibility () by the applied external field (H). Volume

susceptibility is a dimensionless quantity. It can be used to help detectchanges in magnetic properties caused by variations in lithology or byalteration. Magnetic susceptibility was measured at 5-cm intervalsalong the core using a Bartington meter (model MS2C) with an 88-mmcoil diameter and a 2-s integration period. The Bartington meteroperates at a frequency of 0.565 kHz and creates a field intensity of80 A/m (= 0.1 mT), significantly lower than the field intensity neededto change the field orientation of magnetite grains (~50 mT). Thewidth of the instrument response to a thin layer of material with a highmagnetic susceptibility is ~10 cm. For this reason, the first and lastmeasurement of each core section was taken 4 cm from the coresection ends.

Gamma Ray Attenuation Densiometer

The GRA densiometer estimates bulk density by measuring theattenuation of gamma rays traveling through the core from a137Cssource. The gamma rays are attenuated by Compton scattering asthey pass through the sample.

The transmission of gamma raysthrough the sample is related to the electron density of the sample by

Yt

=Yi

x e-nsd,

where

Yt

= the transmitted flux,

Yi

= the incident flux on a scatterer of thicknessd,

n

= the number of scatterers per unit volume or the electron density,and

s

= the cross-sectional area per electron.

The bulk density () of the material is related to the electron density(n) by

n

=x NAV

x (Z/A),

where

Z

= the atomic number or number of electrons,

A

= the atomic mass of the material, and

NAV= Avogadro's number.

Bulk density estimates are therefore

accurate as long as the ratioZ/A

of the constituent elements is approximately constant and correspondsto the ratioZ/A

of the calibration standard. The GRA densiometer wascalibrated to a standard consisting of varying amounts of water andaluminum so that the densities of sediments can be accuratelydetermined. GRA density was measured using a 2-s integration periodat 5-cm intervals along the core.

Compressional Wave (P-Wave) Logger

The compressional wave (P-wave) logger (PWL) measures theultrasonic traveltime of a 500-kHz compressional wave pulse throughthe core and the core liner. A pair of displacement transducersmonitors the separation between theP-wave transducers, and thedistance is used to convert ultrasonic traveltime into velocity aftercorrecting for the liner. Good coupling between the liner and the coreis crucial to obtaining reliable measurements. The PWL is calibrated byplacing a water core between the transducers. The PWL was set totake the mean of 1000 velocity measurements over a

Th, and U are theprimary source of natural gamma rays. These minerals are found inclays, arkosic silts and sandstones, potassium salts, bituminous andalunitic schists, phosphates, certain carbonates, some coals, and acidor intermediate igneous rocks (Serra, 1984). The operation of the NGRis outlined by Hoppie et al. (1994). The NGR system contains fourscintillation counters arranged at 90º angles from each other in aplane orthogonal to the core track. The counters contain doped sodiumiodide crystals and photomultipliers to produce countable pulses. Thetotal response curve of the instrument is estimated to be ~40 cm andso integrates a relatively long length of core in comparison to the otherinstruments of the MST. Natural gamma ray emissions weremeasuredover a 20-s period at 10-cm intervals. The NGR was calibrated in portagainst a thorium source and during Leg 195 by measuring samplestandards at the end of operations at every site.

Thermal Conductivity

Thermal conductivity is the measure of the

rate at which heat flowsthrough a material. It is dependent on the composition, porosity,density, and structure of the material. Thermal conductivity profiles ofsediments and rock sections are used, along with temperaturemeasurements, to estimate heat

flow. Thermal conductivity ismeasured through the transient heating of a core sample with a knowngeometry using a known heat source and recording the change intemperature with time, using the TK04 system described by Blum(1997). For soft sediment, thermal conductivity measurements aremade using a needle probe (Von Herzen and Maxwell, 1959) on whole-core sections; the reported value is the mean of three repeatedmeasurements. For materials too hard for the needle probe topenetrate, thermal conductivity measurements are made after coresplitting, using the needle probe in a half-space configuration(Vacquier, 1985); the reported value is the mean of four repeatedmeasurements. Thermal conductivity measurements were made at aninterval of at least one per core unless variations in lithology requiredmore frequent sampling.

Undrained Shear Strength

The undrained and residual shear strength of sediments andserpentinite mud was measured using a Wykeham-Farrance motorizedvane shear apparatus following procedures described by Boyce (1977).In making vane shear measurements, it is assumed that a cylinder ofsediment is uniformly sheared around the axis of the vane in anundrained condition. The vane used for all measurements has a 1:1length to diameter bladeratio with a dimension of 1.28 cm. A highvane rotation rate of 90°/min was used to minimize pore fluidexpulsion while measurements take place. Torque and strainmeasurements at the vane shaft were made using a torque transducerand potentiometer. Undrained shear strength measurements weremade at least once per core section unless variations in lithologyrequired more frequent sampling.

P-Wave Velocity

DiscreteP-wave velocity measurements were made in three directionsin the sediments using two pairs ofinsertion transducers (PWS1 andPWS2) with fixed separations of 7 and 3.5 cm, respectively, and a pairof contact transducers (PWS3) in a modified Hamilton Frame. PWS1,PWS2, and PWS3 use a 500-kHz compressional wave pulse to measureultrasonic traveltimes, which, when combined with transducerseparation data, can be used to determine velocity. PWS1 and PWS2were only used to measure velocity in soft sediments, where they wereinserted into the face of the split core. PWS1 is aligned with the coreaxis (the

z-direction), and PWS2 is aligned perpendicular to the coreaxis (the y-direction). PWS3 is mounted vertically with one transducerfixed and the other mounted onto a screw, allowing the transducerseparation to be altered. PWS3 measures velocity in the x-direction insplit cores but is also used to measure velocity in discrete samples ofhard sediments or crystalline rock. Distilled water is applied to PWS3to improve the acoustic coupling between the transducers and thesample.P-wave velocity measurements were made at least once percore section.

Index Properties Measurements

Minicore samples of ~10 cm3

were collected using a piston sampler insoft sediment or an electric drill in rocks. Samples were taken at leastonce per section. Sediment samples wereplaced in a 20-mL beakerand sealed to prevent moisture loss. Rock samples were soaked inseawater for 24 hr before determining the wet mass. Samples werethen dried in an oven at 105° ± 5°C for 24 hr and allowed to cool in adesiccator before measuring dry weights and volumes (method C inBlum, 1997). Wet and dry sample masses and dry volumes weremeasured and used to calculate wet bulk density, dry density, graindensity, water content, and porosity. Sample mass was determinedusing two Scientech electronic balances. The balances are equippedwith a computerized averaging system that corrects for shipaccelerations. The sample mass is counterbalanced by a known masssuch that the mass differentials are generally <1 g. Sample volumeswere measured at leastthree times, or until a consistent reading wasobtained, using a helium-displacement Quantachrome penta-pycnometer. A standard reference volume was included with eachgroup of samples during the measurements and rotated among thecells to check for instrument drift and systematic error; each time anerror was detected in the measurement of the reference volume, theoffending cell was calibrated. The following relationships can becomputed from the two mass measurements and dry volumemeasurements (taken from Blum, 1997, pp. 2-2 to 2-3). When abeaker is used, its mass and volume are subtracted from themeasured total mass and volume. This results in the following directlymeasured values:

Variations in pore water salinity (s) and density (pw) that typicallyoccur in marine sediments do not affect the calculations significantly,and standard seawater values under laboratory conditions are used:

s = 0.035 wt% and

pw= 1.024 g/cm3.

Pore water mass (Mpw), mass of solids (Ms), and pore water volume(Vpw) can then be calculated:

Mpw

= (Mb

-

Md)/(1-

s),

Ms

=Mb

-

Mpw

= (Md

-

[s xMb])/(1-

s), and

Vpw

=Mpw

/pw

= (Mb

-

Md)/[(1-

s) xpw].

Additional parameters required are the mass and volume of salt (Msalt

andVsalt, respectively) to account for

the phase change of pore watersalt during drying. It should be kept in mind that for practicalpurposes, the mass of salt is the same in solution and as a precipitate,whereas the volume of salt in solution is negligible. Thus,

Msalt

=Mpw

-

(Mb

-

Md) =[(Mb

-

Md) x s]/(1-

s), and

Vsalt

=Msalt

/salt

= {[(Mb

-

Md) x s]/(1-

s)}/salt,

where the salt density (salt

= 2.20 g/cm3) is a calculated value foraverage seawater salt.

Moisture content is the pore water mass expressed either aspercentage of wet bulk mass or as a percentage of the mass of salt-corrected solids:

The electrical resistivity of the sediment was measured using a four-electrode configuration. The instrument used was modified at theUniversity of California, Santa Cruz, from the design of Andrews andBennett (1981) and was built at the University of Hawaii. Theelectrodes consisted of four stainless steel pins that are 2 mm indiameter, 15 mm in length, and spaced 13 mm apart. A 20-kHzsquare-wave current was applied on the outer electrodes, and thedifference in potential between the two inner electrodes wasmeasured. The size of the current (typically 50 mA) was measuredover a resistor in the outer circuit.

The main purpose of measuring sediment resistivity was to determinethe formation factor, defined as the ratio of the resistivity of sedimentwith included pore water divided by the resistivity of the pore wateralone. In practice, the formation factor is approximated by measuringthe apparent resistivity of the sediment inthe split core liner anddividing that value by the apparent resistivity of seawater of similarsalinity and the same temperature in a 30-cm length of split core liner.Using the same configuration for the measurement of the apparentresistivities removesthe effects of geometry from the determination ofthe formation factor.

Hydraulic Conductivity and Specific Storage

The hydraulic conductivity and specific storage of the serpentinite mudwas measured during a consolidation test. In this test, an axial surfaceload is applied to a laterally constrained sample. The axial loadproduces an excess pore fluid pressure along the length of the core.The bottom of the sample is drained so that the excess pore fluidpressure at that point is zero. The loads and boundary conditions areapplied by a Manheim squeezer, and the amount of fluid displaced ismeasured as a function of time. FigureF10

is a cartoon of theapparatus and the boundary conditions. Also shown is the pressureprofile along the length of the sample at various times. Theassumption of incompressible mineral grains and water, common tosoil mechanics (Wang, 2000), allows the volume of water discharged

from the sample to be converted to axial displacement using the cross-sectional area of the sample. Because the frame, not the mineralgrains or the water, is compressed, we can calculate the axialdisplacement using the following equation:

w

= volume of water discharged/cross-sectional area of sample,

wherew

= the axial displacement. We then use the relationship fordisplacement in an infinite length cylinder as a function of time (Wang,2000):

,

to determine the lumped product of constants (on the right hand sideof the following equation) by plotting the slope of the displacementover the square root of time

,

where

cm

= the vertical compressibility,

= the loading efficiency,

z

= the axial load, and

D

= the hydraulic diffusivity.

FigureF11

compares experimentally determined displacements withcalculated displacements as a function of time. Only the early timeportion of the plot is used to determine the lumped product ofconstants. Early in the experiment, the decrease in pore pressure hasnot yet diffused to the end of the sample and so the approximation ofan infinite cylinder is still valid. To determine the hydraulic diffusivity(D) from the lumped product, we need to determine the otherunknown factors,cm

and.

The vertical compressibility is defined by

.

Because all the components of the equation above, axial displacement(w), axial stress (z), and sample length (wo) are measured, it ispossible to calculate the vertical compressibility. Also, because thepore pressure throughout the entire length of the sample returns tozero at very long times, the boundary condition of no change in porepressure (Ppore